Rise in cases of Clade II Mpox and Clade I Mpox Virus detected in wastewater

Current situation

Mpox (formerly "monkeypox"), the infection caused by the mpox virus (MPXV), has been circulating at low levels in Washington State since the 2022 global outbreak of clade II mpox. We have recently seen an increase in clade II mpox cases in the Puget Sound Area associated with sexual and intimate contact among gay, bisexual, and other men who have sex with men, transgender people, and non-binary people. In September 2025, there were 35 cases diagnosed in King County, the largest number of new diagnoses in a month since the end of the 2022 outbreak.

In addition, the WA DOH has been monitoring for a potentially more severe strain of mpox (clade I) since 2024. An outbreak of clade I mpox is ongoing in Central and East Africa and several travel-related clade I mpox cases have been reported in other states. On September 24th, 2025, WA DOH and Tacoma-Pierce County Health Department (TPCHD), working in collaboration with the University of Washington, detected clade I MPXV in wastewater in Pierce County. WA DOH has not yet been notified of a case of clade I mpox, and the risk to the community remains low.

Actions requested

• Immediately report all suspected cases of mpox to PHKSC.
• Consider mpox on your differential for any patients with signs and symptoms of mpox, even if:
  • Diagnosis of syphilis or herpes is considered more likely (co-infections can occur)
  • The patient has a history of mpox vaccination. Mpox infections in people who previously received one or more vaccine doses are usually:
    • Less severe
    • May present subtly as proctitis without anogenital lesions, or with only a few lesions
    • May present without prodromal constitutional symptoms.
• Consider the possibility of clade I mpox in persons with a recent travel history to Central or East Africa or contact with a confirmed or suspected case of clade I mpox
  • There is no clinical distinction in the signs and symptoms of clade I mpox and clade II mpox.
• Test for mpox:
  • Testing may be available through your facility's clinical or commercial laboratory.
  • If possible, choose a PCR test option that includes clade determination testing.
  • Follow mpox specimen collection guidelines for your facility, or refer to specimen collection guidelines from WA DOH.
  • If you do not have access to clade determination testing and suspect clade I mpox, contact PHSKC to request testing at the WA Public Health  Laboratories (PHL).
    • Do NOT send specimens to the PHL without prior approval from PHSKC.
• Continue to vaccinate individuals who are eligible to receive mpox vaccination.
  • Mpox vaccine is effective against both mpox clades.
  • Booster doses are currently not recommended by the CDC if someone has already completed their series.
  • Obtain vaccine from commercial suppliers.
    • WA DOH offers limited doses of JYNNEOS vaccine to clinics who serve individuals for whom vaccine is recommended (see Mpox Vaccine  Opportunity).
• Offer the mpox vaccine as post-exposure prophylaxis (PEP) to individuals who have had direct contact with someone with mpox. PEP is effective against both mpox clades.
  • Encourage patients to work with PHSKC or other local health jurisdictions to connect close contacts and sexual partners to PEP.
  • PEP should be offered as soon as possible after exposure to someone with mpox:
    • Within 4 days of exposure to prevent illness.
    • Up to 14 days after exposure to reduce risk of severe disease.
• Treatment and management for patients with clade I mpox is the same for clade II.
  • Most immunocompetent patients with mpox will improve with supportive care alone.
  • Mpox treatment is available under the CDC's Investigational New Drug Protocol for qualifying patients who are immunosuppressed or have severe disease.
  • Contact PHSKC and/or WA DOH at mpoxconsult@doh.wa.gov for assistance with evaluating need for therapeutics.
• Offer HIV and syphilis testing, mpox vaccination, HIV pre-exposure prophylaxis (PrEP), and doxy-PEP to patients who are gay or bisexual men, or the sex partners of gay or bisexual men.
• Travel health providers should conduct a sexual health history with patients and offer mpox vaccination to travelers visiting a country with sustained clade I mpox transmission regardless of the patient's gender identity or sexual orientation, if they anticipate experiencing any of the following:
  • Sex with a new partner,
  • Sex at a commercial sex venue, like a sex club or bathhouse,
  • Sex in exchange for money, goods, drugs, or other trade,
  • Sex in association with a large public event or festival.